A Constraint On The Formation Of Dwarf Elliptical Galaxies In The Dense Coma Cluster Core

Deep CCD photometry and positions for a new sample of ≃ 250 dwarf elliptical (dE) galaxies in the Coma cluster core are analyzed. A significant color gradient is detected in their projected radial distribution, given by ∆(B–R)/∆(logRcc) = −0.08± 0.02 mag. Calibrating these dE galaxies against Galactic globular clusters yields a corresponding metallicity gradient which goes as Z ∝ R cc . Simulations reveal that this gradient in the projected radial distribution corresponds to a true (three-dimensional) radial color gradient which goes as ∆(B–R)/∆(log r) ≃ −0.20 mag, or Z ∝ r, over the same radial range. If this radial gradient is a primordial one, it is consistent with a model in which the intracluster gas exerted a significant confinement pressure, impeding the outflow of supernovae-driven metal-rich gas from the young dE galaxies. Subject headings: galaxies: clusters: individual (Coma) — galaxies: dwarf: elliptical and lenticular, cD — galaxies: formation — galaxies: evolution